Embryology; Head, Face & Oral Cavity Revision PDF

Embryology; head, face & oral cavity  Embryogenesis = Embryology = Oral embryology = Derivatives =...

Embryology; head, face & oral cavity  Embryogenesis = Embryology = Oral embryology = Derivatives = Process of The study of the The study of the Structures that the embryological development of development of oral origins/tissue layers development, forming tissues. tissues. form. of tissues and organs. Ectoderm = Mesoderm = Endoderm = Outside layer for Middle layer for Inside layer for protection. support. (Muscles, specialist organs. (Enamel, skin, blood, bone, (Digestive, nails) connective tissue) respiratory systems) Early embryogenesis: Weeks 1–4 Week 1: Fluid filled Blastocyst with Embryoblast (70-100 cells). (Fertilisation-cleavage-proliferation-migration-differentiation) Week 2–3: Embryoblast proliferates and forms bilaminar embryonic disc (Ectoderm & endoderm). Proliferates again into trilaminar embryonic disc Ectoderm, mesoderm & endoderm). EMBRYONIC ORIGINS FORMED Week 3–4: Highly specialised neural crest cells (derivatives from ectoderm and neuroectoderm), form ectomesenchyme. Week 4: Embryo starts to fold; stomodeum (primitive mouth), bucco-pharyngeal membrane, primitive gut. The bucco-pharyngeal membrane ruptures to allow for stomodeum and gut communication. Embryo develops bulges; pharyngeal (branchial) arches. Each arch has its own nerve and blood supply and cartilage.  Pharyngeal arches and derivatives Arch Nerves Blood Muscles Cartilage Bone 1st (I) Trigeminal nerve 1st aortic arch Muscles of Merkel’s -Mandible Mandibular (V cranial nerve) mastication -Maxilla arch -Zygomatic -Temporal (squamous) 2nd (II) Hyoid Facial nerve 2nd aortic Muscles of Reichert’s -Hyoid arch (VII cranial nerve) arch facial -Styloid expression 3rd (III) arch Glossopharyngeal 3rd aortic arch Stylopharyngeal None -Hyoid nerve muscle -Thymus (IX cranial nerve) (Swallowing) connective tissue -Inferior parathyroid 4th (IV) arch Vagus nerve 4th aortic arch Laryngeal Larynx -Thyroid (X cranial nerve) muscles Superior laryngeal branch Embryogenesis: Weeks 5–8 Week 4–6: Face develops. (1x frontonasal, 2x maxillary, 2x mandibular prominences). Week 4–7: Tongue develops; Anterior 2/3 1st & 2nd pharyngeal arch, Posterior 1/3 4th arch. (Fills space where secondary palate will form). Cellular apoptosis allows tongue to separate from floor of mouth. Week 6–7: Primary palate forms at same time as face. (Frontonasal and medial nasal prominences fuse together). Week 7–8: Secondary palate forms after primary palate. Palatine shelves fuse along midline with primary palate and nasal septum. Week 7: Development of alveolar bone and skull, maxilla and mandible jaws undergo ossification. Fetal development: Week 9–Birth Begins after first 8 weeks of development. Growth of the fetus. Development and maturation of structures that have formed. Fetus can now move limbs. Aetiology of anomalies Genetic — single gene defects and/or genetic variant/defect. Environmental (congenital) — infections, radiation, hormones, nutritional deficiencies, medications etc. Clinical significance Interruptions may result in developmental anomalies — higher risk of oral disease and impact on tooth development. If cellular apoptosis didn’t occur, the patient would be ‘tongue-tied’, (Ankyloglossia) — Impacts; oral hygiene, speech, feeding and breathing. Cleft lip and/or palate — congenital anomalies — Impacts; oral hygiene, feeding, speech, hearing and development. Cleft lip (CL) = Cleft palate (CP) = Failure of fusion of 2 Failure of fusion of mesial nasal palatine shelves processes and/or together and/or maxillary and mesial nasal septum. nasal processes. Cleft lip & palate (CLP) = Combination of CL and CP.